The human milk oligosaccharide LNT has previously been crystallized. Kuhn et al. [Chem. Ber. 86, 827, (1953)] isolated LNT from mother's milk for the first time and crystallized it from aqueous ethanol. Upon drying, the air-dried crystalline material lost more than 10% of its weight (melting point 200-205° C. (dec.)), but its crystal structure did not change according to X-ray power diffraction measurements. The so-dried material proved to be hygroscopic as it took back around 8% of its weight when stored in air. Later, the same authors reported the obtention of crystalline LNT by partial hydrolysis of lacto-N-fucopentaose I [Chem. Ber. 89, 2514 (1956)] or sialylated LNT [Chem. Ber. 95, 513 (1962)], both isolated from mother's milk, followed by crystallization; their reported decomposition points were 205±10° C. (“depending on water content and the speed of heating”) and 211-214° C., respectively; both samples were considered to be identical with the previously reported one based on their X-ray power diffractogram and/or IR spectrum. Similarly, Malpress et al. [Biochem. J. 68, 708 (1958)] isolated LNT from mother's milk having a melting point of 204-205° C. Takamura et al. [Chem. Pharm. Bull. 27, 1497 (1979) and ibid. 28, 1804 (1980)] reported a melting point of 225-228° C. for LNT made by chemical total synthesis and crystallized from aqueous ethanol.
Crystallization or recrystallization is one of the simplest and cheapest methods to separate a product from contaminants and obtain a pure substance. Providing alternative crystalline forms of a solid compound is an important aspect of the product's development, because the different crystalline forms affect the compound's properties—for example, thermodynamic stability, solubility, density, hygroscopicity, electrical properties (such as dielectric constant, conductivity), mechanical properties (such as friability, hardness, breaking strength, elasticity), optical properties (such as colour, transparency, refraction), etc.—diversely. Polymorphs or other crystalline forms provide alternative means for improving a product's characteristics and usefulness.
For this reason, ways have been sought for obtaining other crystalline forms of LNT which have different, preferably advantageous, physical properties (such as e.g. hygroscopicity, stability, dissolution rate, purity, filterability, drying properties, flowability of the powder, etc.) for facilitating its isolation from a complex milieu or its use in pharmaceutical or nutritional compositions.